1. Field of the Invention
The invention relates to a pump, in particular, for pumping fuel in an internal combustion engine of a motor vehicle, the pump comprising a housing in which a shaft is rotatably supported.
2. Description of the Related Art
Conveying pumps are known which continuously convey fuel, in particular, diesel fuel, from a tank into a reservoir. The cylinders of the internal combustion engine are connected to the reservoir by solenoid valves. The greater portion of the fuel is returned from the reservoir into the tank by means of pressure limiting valves because only a small portion of the continuously conveyed fuel is required for the internal combustion process in the cylinders. The continuous return of the fuel results in unsatisfactory efficiency. As a result of the continuous conveying and return action, a great heat development is also observed. Accordingly, it is not possible to employ a plastic material for such a pump; it is necessary to employ metal which is more expensive.
For conveying the fuel it is also known to provide a vacuum throttle. Check valves ensure that a sufficient amount of fuel is always available for the combustion process. The check valves or their springs have however tolerances so that different amounts of fuel will enter the cylinders. As a result of the variable degree of filling, high pulsations occur which result in a strong noise development. Also, the mechanical loading of the motor cylinders and their pistons is very high. In order to maintain a relatively small amount of fuel in circulation, proportional solenoid valves are adjusted to a middle position so that only a portion of the fuel is conveyed. As a result of tolerances of the springs of the proportional solenoid valves, different amounts of fuel are present in the piston chamber. During the vacuum process vapor bubbles are formed in the piston chamber which are quickly compressed upon return of the piston. However, since fuel cannot be compressed, the piston is thus greatly slowed down so that this results in high mechanical loading. By means of the proportional solenoid valves, it is possible to supply per time unit the same amount of fuel, respectively. However, since the amount of fuel for the internal combustion process depends on the engine speed (rpm) of the motor, the proportional solenoid valves must be controlled in a complicated fashion as a function of the rpm of the motor.
It is an object of the present invention to configure the pump of the aforementioned kind such that it has a good efficiency and conveys reliably the amount of fuel required for the internal combustion process.
In accordance with the present invention, this is achieved in that the eccentricity of an eccentric drive can be adjusted by means of the shaft, wherein the eccentric drive is provided for driving at least one drive element which is adjustable according to the adjusted eccentricity by a translatory movement in a plane positioned transverse to the shaft.
In the pump according to the invention, the drive element is driven by means of the eccentric drive. Depending on the eccentricity of the eccentric drive, the drive element is moved or adjusted by a translatory movement to varying degrees in a plane positioned transversely to the shaft. With this measure, it is, for example, possible to adjust in a continuous manner the stroke of a piston from zero to a maximum value by means of the drive element, for example, in order to convey a corresponding amount of fuel into the internal combustion chamber of the motor cylinder. Since the eccentric drive is coupled with the shaft, the eccentricity can be adjusted in a simple way as a function of the rpm of the internal combustion engine. The eccentric drive makes possible a compact configuration of the pump. It is suitable especially for common rail systems.